I verified this on Windows 8.1 and Mac OS X: the label for "Full Screen" does not wrap, and you can see there are other labels, much longer, that wrap correctly. I have Linux only as a virtual machine, font is pretty small so the text is displayed completely.

This is because it's a toggle type button. We're going to hit this with any button that declares a type of its own, because we're extending the XBL binding in order to have the label wrap, as button labels don't wrap by default. Blegh. Not really sure what, if anything, can be done here. I don't think extending all the existing bindings to also have a drag type (and swapping bindings when entering/exiting the panel for all of them) is sensible. I'd prefer if we had an attribute/property that was recognized for all toolbarbuttons. Dão, does that sound workable, or do you see another/better solution?

The issue applies to Slovak locale as well and since the "Full Screen" is a pretty much standardized term there is no way to shorten the translation, unless we are confident with decreasing an user experience (I'm not at all)

See bug 944947 comment 12.

This should be fixed on tomorrow's nightlies by the patches from bug 944947.